ECG and QTc monitoring on antipsychotics

Antipsychotics can affect the heart's electrical recovery time, measured on an ECG as the QT interval. When QT (corrected for heart rate, called QTc) gets long enough, the risk of a dangerous arrhythmia called torsades de pointes goes up. ECG monitoring on antipsychotics is targeted, not universal, and understanding when it matters takes the mystery out of the test.

What the QT interval measures

The QT interval on an ECG is the time from the start of ventricular depolarisation to the end of repolarisation — essentially how long it takes the heart to electrically reset between beats. Because QT shortens at faster heart rates, it is corrected mathematically (QTc) to allow comparison across rates. Several formulas exist (Bazett, Fridericia); most modern ECG machines provide a QTc automatically.

What is "long"?

• Normal: QTc < 450 ms in men, < 460 ms in women
• Borderline: 450–470 ms (men), 460–480 ms (women)
• Prolonged: 470–500 ms — caution, monitor
• High-risk: > 500 ms — strongly consider stopping or switching the offending drug
• Significant change: an increase of > 60 ms from baseline, even if absolute value is acceptable

Antipsychotic risk tiers for QT

• Higher risk: ziprasidone, thioridazine (now rarely used for this reason), pimozide, IV haloperidol, IV droperidol, chlorpromazine, sertindole (not US-marketed)
• Moderate: iloperidone, asenapine, quetiapine, risperidone, paliperidone, oral haloperidol
• Lower: aripiprazole, brexpiprazole, lurasidone, lumateperone, cariprazine, olanzapine, clozapine

Even "lower risk" agents can prolong QT in the right patient with the right combination of other risks.

When to get a baseline ECG

The American Psychiatric Association and most expert reviews recommend a baseline ECG when:

• The chosen antipsychotic carries notable QT risk (especially ziprasidone, IV haloperidol, pimozide, IV droperidol)
• The patient has personal or family history of QT prolongation, syncope, or sudden cardiac death
• The patient has structural heart disease, heart failure, or recent MI
• The patient is taking other QT-prolonging drugs (some antibiotics, antifungals, antiarrhythmics, methadone)
• The patient has electrolyte disturbances (low potassium, low magnesium)
• The patient is older or has eating disorders, dehydration, or significant medical comorbidity

For low-risk antipsychotics in healthy young patients with no risk factors, a baseline ECG is often omitted.

Follow-up ECGs

If a baseline ECG was obtained because of a higher-risk drug or patient, follow-up ECGs are typically performed:

• After reaching the target dose
• After significant dose increases
• When a new QT-prolonging medication is added
• When a new electrolyte disturbance is identified
• If symptoms suggesting arrhythmia occur (palpitations, syncope, near-syncope)

What to do with an abnormal QTc

• Borderline (450–500 ms): address modifiable factors — correct potassium and magnesium, stop or substitute other QT-prolonging drugs where possible, lower dose if clinically possible.
• ≥ 500 ms or increase > 60 ms: usually warrants reducing or stopping the offending drug and switching to a lower-risk agent. Cardiology consultation is reasonable.
• Symptoms (syncope, palpitations): urgent evaluation regardless of QTc number.

Drug-drug interactions to flag

Common QT-prolonging or risk-amplifying drugs to discuss with the prescriber include:

• Macrolide antibiotics (azithromycin, clarithromycin, erythromycin)
• Fluoroquinolones (especially moxifloxacin, levofloxacin)
• Azole antifungals (fluconazole, voriconazole)
• Methadone
• Class III antiarrhythmics (amiodarone, sotalol)
• Some antiemetics (ondansetron at higher doses)
• Some antidepressants (citalopram > 40 mg/day)

Crediblemeds.org maintains a regularly updated list at crediblemeds.org.

Ziprasidone and the FDA conversation

The FDA Geodon (ziprasidone) label includes specific QT cautions and recommends ECG monitoring in patients with relevant risk factors. Ziprasidone is one of the antipsychotics most likely to trigger pre-treatment ECG screening.

Practical questions to ask your prescriber

• Do I need a baseline ECG for this medication?
• What was my baseline QTc?
• What other medications I take could affect QT?
• Should we check potassium and magnesium today?

The big picture

QT monitoring is one of the more nuanced parts of antipsychotic care. The test is fast and non-invasive. The risk of a serious arrhythmia is small for most people on most antipsychotics, but the consequences are large enough that targeted screening is the standard of care. Knowing where your medication falls on the risk spectrum, and what your baseline number is, takes a lot of the worry out of the conversation.

This article is for educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a qualified mental health professional. If you or someone you know is in crisis, call or text 988 in the US, or your local emergency number.